Photovoltaic element and a method for manufacturing the same

ABSTRACT

In a photovoltaic element according to the present invention, a first transparent conductive film, a second transparent conductive film, a p-type semiconductor film, an intrinsic semiconductor layer, a n-type semiconductor layer and a backside electrode are stacked in turn on a transparent substrate. Then, an intermediate layer is provided between the second transparent conductive film and the p-type semiconductor layer so as to cover the first transparent conductive film and the second transparent conductive film.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention:

[0002] This invention relates to a photovoltaic element and a method formanufacturing the same, particularly to a photovoltaic element and amanufacturing method of the photovoltaic element which are suitable forsemiconductor elements to constitute a solar battery.

[0003] 2. Related Art Statement

[0004] Attention has been paid to a thin film solar battery formed by avapor phase epitaxy method, and various research and development arecarried out for the thin film solar battery. Generally, the thin filmsolar battery is composed of a photovoltaic element in which atransparent conductive film, a first conduction-type semiconductorlayer, an intrinsic semiconductor layer and a second conduction-typesemiconductor layer are stacked on a transparent substrate in turn.

[0005]FIG. 1 is a structural view showing a conventional photovoltaicelement.

[0006] In a photovoltaic element 10 depicted in FIG. 1, a transparentconductive film 2, a p-type semiconductor layer 3, an intrinsicsemiconductor layer 4, a n-type semiconductor layer 5 and a backsideelectrode 6 are stacked on a transparent substrate 1.

[0007] The transparent substrate 1 is composed of a glass substrate or aresin film made of polyethylene naphthalate (PEN), polyethersulfone(PES), polyethylene terephthalate (PET) or the like.

[0008] The transparent conductive film 2 is formed, of tin oxide, ITO,ZnO or the like, in a thickness of about 1 μm or below by sputtering orfiring.

[0009] The p-type semiconductor layer 3, the intrinsic semiconductorlayer 4 and the n-type semiconductor layer 5 are formed in a thicknessof about 1 μm or below by plasma CVD, etc. These semiconductor layersinclude a Si semiconductor material as a base matrix. The p-typesemiconductor layer also includes a dopant such as B, and the n-typesemiconductor layer also includes a dopant such as P.

[0010] The backside electrode 6 is formed, of a metallic material suchas Al, Ag, or Ti, in a thickness of about 100 μm or below by sputteringor evaporation.

[0011] However, the photovoltaic element 10 has the transparentconductive film 2, on which the above semiconductor layers are formed,and therefore, has a lower open circuit voltage (Voc) than that of aphotovoltaic element having a metallic electrode on which the abovesemiconductor layers are formed.

SUMMARY OF THE INVENTION

[0012] It is an object of the present invention to repress thedegradation of the open circuit voltage (Voc) in the photovoltaicelement including the substrate, the transparent conductive film, thefirst conduction-type semiconductor layer, the intrinsic semiconductorlayer and the second conduction-type, different from the above firstconduction-type, semiconductor layer.

[0013] For achieving the above object, this invention relates to aphoto-voltaic element including a substrate, a transparent conductivefilm provided on the substrate, an intermediate layer, provided so as tocover the transparent conductive film, made in a hydrogen gas atmosphereof 15 volume % or below hydrogen concentration, a first conduction-typesemiconductor layer provided on the intermediate layer, an intrinsicsemiconductor layer provided on the first conduction-type semiconductorand a second conduction-type, different from the first conduction-type,semiconductor layer provided on the intrinsic semiconductor layer.

[0014] Moreover, this invention also relates to a method formanufacturing a photovoltaic element comprising the steps of forming atransparent conductive film on a substrate, forming an intermediatelayer so as to cover the transparent conductive film in a hydrogen gasatmosphere of 15 volume % or below hydrogen concentration, and forming,on the intermediate layer, a first conduction-type semiconductor layer,an intrinsic layer and a second conduction-type, different from thefirst conduction-type, semiconductor layer in turn.

[0015] The present inventors have intensely studied the causes that theopen circuit voltage (Voc) of the photovoltaic element having thesemiconductor layers on the transparent conductive film is smaller thanthat of the photovoltaic element having the same semiconductor layers onthe metallic electrode. As a result, they have considered the cause asfollows.

[0016] Spear et al. found out by chance that the addition of a smallamount of phosphor element or boron element to an amorphous siliconincorporating hydrogen elements changes the properties of the amorphoussilicon drastically. Ever since, the silicon semiconductor is made byplasma CVD using a raw material gas such as silane gas and a hydrogengas for realizing the various properties thereof. Moreover, more amountof hydrogen than the requisite amount for forming the amorphous siliconsemiconductor is applied to a film-forming atmosphere, thereby tomicronize the crystal grains of the amorphous silicon semiconductor.

[0017] Then, it is required in a semiconductor manufacturing process tosupply relatively large amount of hydrogen to form much hydrogen plasma,and to resolve and deposit a raw material gas such as silane gas by thehydrogen plasma. Therefore, the hydrogen radical elements incorporatedin the hydrogen plasma may reduce the transparent conductive film, andseparate metallic elements such as indium elements or zinc elements.Then, the separated metallic elements may exist on the boundariesbetween the transparent conductive film and the p-type semiconductorlayer, and degrade the open circuit voltage (Voc) through thedeterioration of the boundary condition.

[0018] Therefore, the present inventors has made an attempt to make thetransparent conductive film of an oxide material mainly incorporatingplasma-proof zinc oxide or cover the transparent conductive film havinga smaller resistance with the plasma-proof transparent conductive film.Concretely, a thin zinc oxide film, having a smaller conductivity andreduction sensitivity, is formed on the transparent conductive film madeof tin oxide or ITO, and then, the semiconductor layers are formed onthe thin zinc oxide film.

[0019] However, the above attempt can not repress the reduction of thetransparent conductive film. Moreover, the thin zinc oxide film isformed at room temperature by a cheap sputtering apparatus because ahigh temperature sputtering requires an expensive apparatus. Therefore,the thin zinc oxide film tends to have an amorphous structure, sosuffers from the reduction thereof with comparison to the crystallinezinc oxide.

[0020] Moreover, it is desired to use a flexible polymer film as thesubstrate because the polymer film can be produced on a large scale.However, since the polymer film is vulnerable to heating, thetransparent conductive film is required to be formed at low temperature.Therefore, the transparent conductive film results in having anamorphous structure.

[0021] Furthermore, the present inventors made an attempt to form thesemiconductor films on the transparent conductive film by inert gasplasma instead of hydrogen gas plasma for preventing the reduction ofthe transparent conductive film. In this case, however, the photovoltaicelement has only a small open circuit voltage (Voc). Although the reasonis unclear, it is considered as the number of the dangling bond of thep-type semiconductor layer on the transparent conductive film increases.

[0022] Therefore, the inventors paid attention to the layer structure ofthe photovoltaic element instead of the manufacturing method for thephotovoltaic element.

[0023] As a result, the inventors found out that by forming anintermediate layer between the transparent conductive film and thep-type semiconductor layer under a hydrogen concentration atmosphere of15 volume % or below so as to cover the transparent conductive film, thedegradation of the open circuit voltage (Voc) can be repressed. That is,it is considered that the intermediate layer repress the reduction ofthe transparent conductive film.

[0024] In a preferred embodiment of the photovoltaic element of thepresent invention, an interfacial layer is formed between the firstconduction-type semiconductor layer and the intrinsic semiconductorlayer. The interfacial layer may improve the boundary condition betweenthe first conduction-type semiconductor layer and the intrinsicsemiconductor layer, so that the open circuit voltage (Voc) of thephotovoltaic element can be enhanced.

[0025] In the case of manufacturing the photovoltaic element having theinterfacial layer, the above manufacturing method further includes thesteps of forming the interfacial layer between the first conduction-typesemiconductor layer on the first conduction-type semiconductor layer andforming the intrinsic semiconductor layer on the interfacial layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] For a better understanding of this invention, reference is madeto the attached drawings, wherein:

[0027]FIG. 1 is a structural view showing a conventional photovoltaicelement,

[0028]FIG. 2 is a structural view showing a photovoltaic elementaccording to the present invention,

[0029]FIG. 3 is a structural view showing another photovoltaic elementaccording to the present invention,

[0030]FIG. 4 is a graph showing a Raman spectroscopic analysis spectrumof a photovoltaic element according to the present invention,

[0031]FIG. 5 is a graph showing a Raman spectroscopic analysis spectrumof a photovoltaic element according to the present invention,

[0032]FIG. 6 is a graph showing a comparative Raman spectroscopicanalysis spectrum with that of a photovoltaic element according to thepresent invention, and

[0033]FIG. 7 is a graph showing a comparative Raman spectroscopicanalysis spectrum with that of a photovoltaic element according to thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0034]FIG. 2 is a structural view showing a photovoltaic elementaccording to the present invention.

[0035] In a photovoltaic element 20 shown in FIG. 2, a first transparentconductive film 12-1, a second transparent conductive film 12-2, ap-type semiconductor film 13, an intrinsic semiconductor layer 14, an-type semiconductor layer 15 and a backside electrode 16 are stacked inturn on a transparent substrate 11. Then, an intermediate layer 17 isprovided between the second transparent conductive film 12-2 and thep-type semiconductor layer 13 so as to cover the first transparentconductive film 12-1 and the second transparent conductive film 12-2.

[0036] It is required that the intermediate layer 17 is formed under ahydrogen gas atmosphere of 15 volume % or below concentration,preferably 6 volume % or below concentration. Thereby, the reduction ofthe first transparent conductive film 12-1 and the second transparentconductive film 12-2, which are positioned under the intermediate layer14, may be repressed, and thus, the open circuit voltage (Voc) can beenhanced. As a result, the photovoltaic element 20 can have the opencircuit voltage (Voc) equal to that of a photovoltaic element having ametallic electrode on the transparent substrate in place of the abovetransparent conductive film.

[0037] Moreover, the intermediate layer 17 may be formed under ahydrogen atmosphere of a minute concentration, for example, at least 1volume % concentration, preferably at least 2 volume % concentration.

[0038] It is desired that the intermediate layer 17 is formed, under theabove hydrogen atmosphere, by a CVD method, particularly by a plasma CVDmethod for enhancing the properties of the intermediate layer 17.

[0039] Although the intermediate layer 17 may be used without anypost-treatment, it is desired that a surface 17A of the intermediatelayer 17 is plasma-treated under a hydrogen-reduction atmosphere. Inthis case, even though the intermediate layer 17 has an amorphousstructure, the p-type semiconductor layer 13 to be formed on theintermediate layer 17 can be micro-crystallized. As a result, theshort-circuit current (Isc) of the photovoltaic element 20 can beenhanced.

[0040] The above hydrogen reduction atmosphere includes 50-100 volume %concentration, preferably 80-100 volume % concentration, and is set to apressure range within 1.333-1333 Pa. Then, an electric power of 30-600mW/cm³ with a high frequency wave of 13.56 MHz, for example, is appliedto the hydrogen reduction atmosphere to generate a hydrogen plasma forplasma-treating the surface 17A of the intermediate layer 17.

[0041] The intermediate layer 17 may be made of any kind of material,but preferably made of the same semiconductor material as that of anyone of the above semiconductor layers 13, 14 and 15. If the abovesemiconductor layers 13, 14 and 15 are made of a cheap silicon material,the intermediate layer 17 is also made of the silicon material. In thiscase, the manufacturing process of the photovoltaic element 20 can besimplified as mentioned below.

[0042] In the case of making the intermediate layer 17 of the siliconmaterial, the intermediate layer 17 is preferably set to be a thicknessof 0.5-15 nm, particularly to a thickness of 1-8 nm. If the thickness ofthe intermediate layer 17 is smaller than 0.5 nm, the photovoltaicelement 20 may not exhibit the above-mentioned advantageous effect ofthe present invention. If the thickness of the intermediate layer 17 islarger than 15 nm, the series resistance of the photovoltaic element 20may be increased, resulting in the reduction of a current in thephotovoltaic element 20.

[0043]FIG. 3 is a structural view showing another photovoltaic elementaccording to the present invention. In FIG. 3, the same references aregiven to the similar parts to the ones of the photovoltaic element 20shown in FIG. 2.

[0044] In a photovoltaic element 30 shown in FIG. 3, a first transparentconductive film 12-1, a second transparent conductive film 12-2, ap-type semiconductor film 13, an intrinsic semiconductor layer 14, an-type semiconductor layer 15 and a backside electrode 16 are stacked inturn on a transparent substrate 11. Then, an intermediate layer 17 isprovided between the second transparent conductive film 12-2 and thep-type semiconductor layer 13 so as to cover the first transparentconductive film 12-1 and the second transparent conductive film 12-2.Moreover, an interfacial layer 18 is provided between the p-typesemiconductor layer 13 and the intrinsic semiconductor layer 14.

[0045] Since the photovoltaic element 30 has the interfacial layer 18between the p-type semiconductor layer 13 and the intrinsicsemiconductor layer 14 in addition to the intermediate layer 17 betweenthe second transparent conductive film 12-2 and the p-type semiconductorlayer 13, it can have more enhanced open circuit voltage (Voc).

[0046] The intermediate layer 17 is made by the same manner as in thephotovoltaic element 20 shown in FIG. 2.

[0047] The interfacial layer 18 may be made of any kind of material, butpreferably made of the same semiconductor material as that of any one ofthe above semiconductor layers 13, 14 and 15. If the above semiconductorlayers 13, 14 and 15 are made of a silicon material, the interfaciallayer 18 is also made of the silicon material. In this case, themanufacturing process of the photovoltaic element 30 can be alsosimplified as mentioned below.

[0048] In the case of making the interfacial layer 18 of the siliconmaterial, the intermediate layer 18 is preferably set to be a thicknessof 0.5-8 nm, particularly to a thickness of 1-4 nm. If the thickness ofthe interfacial layer 18 is smaller than 0.5 nm, the photovoltaicelement 30 may not exhibit the above-mentioned advantageous effect ofthe present invention. If the thickness of the interfacial layer 18 islarger than 8 nm, the series resistance of the photovoltaic element 30may be increased, resulting in the reduction of a current in thephotovoltaic element 30.

[0049] It is desired that the p-type semiconductor layer 13, theintrinsic semiconductor layer 14 and the n-type semiconductor layer 15are formed by a well-known film-forming technique such as a plasma CVDmethod under a hydrogen gas atmosphere of 70-99.8 volume % concentrationfor enhancing the short-circuit current through the micronization of thecrystal grains of those semiconductor layers.

[0050] Although those semiconductor layers 13, 14 and 15 may be made ofany kind of semiconductor material, they are preferably made of thesilicon material as mentioned above because the silicon material ischeap. The p-type semiconductor layer 13 includes dopants such as boronelements in the silicon base matrix, and the n-type semiconductor layer15 includes dopants such as phospher elements in the silicon basematrix.

[0051] Next, the manufacturing process of the above photovoltaicelements 20 and 30 will be explained below.

[0052] Generally, the p-type semiconductor layer 13, the intrinsicsemiconductor layer 14 and the n-type semiconductor layer 15 are formed,by in-line system, in different chambers for preventing thecontamination of the dopant gases for the p-type and the n-typesemiconductor layers 13 and 15. The p-type semiconductor layer 13 andthe n-type semiconductor layer 15 usually have a thickness of severalten nm to 50 nm, respectively, and the intrinsic semiconductor layerusually have a thickness of 500-1000 nm. Therefore, it takes longer timein the forming process of the intrinsic semiconductor layer 14 than thatof the p-type and the n-type semiconductor layers 13 and 15.

[0053] As a result, while the intrinsic semiconductor layer is formed onan assembly on an advanced manufacturing step, another assembly on aprevious manufacturing step is waited for a given period until theintrinsic semiconductor layer 14 is formed after the p-typesemiconductor layer 13. Therefore, it is desired that the intermediatelayer 17, the p-type semiconductor layer 13 and the interfacial layer 18are formed in the same chamber. In this case, the intermediate layer 17,the p-type semiconductor layer 13 and the interfacial layer 18 can beformed during the waiting period for the manufacturing step of theintrinsic semiconductor layer 14, and thus, the photovoltaic elements 20and 30 can be manufactured efficiently without the prolongation of thelead time of the manufacturing process.

[0054] Even though the intermediate layer 17 and the interfacial layer18 incorporate a small amount of dopant element, they can exhibit theirrespective functions sufficiently.

[0055] If the intermediate layer 17, the p-type semiconductor layer 13and the interfacial layer 18 are made of the same material as mentionedabove, they can be formed easily in the same chamber with supplying thesame raw material gas continuously. Therefore, the photovoltaic elements20 and 30 can be manufactured efficiently as mentioned above.

[0056] In the case of making the intermediate layer 17, the p-typesemiconductor layer 13 and the interfacial layer 18 of the samematerial, a hydrogen gas is introduced into the vacuum chamber, and theintermediate layer 17 is formed under the hydrogen gas atmosphere of agiven hydrogen concentration. After the hydrogen concentration isadjusted to a predetermined concentration, the p-type semiconductorlayer 13 is formed with supplying a dopant gas under the hydrogen gasatmosphere. After the supply of the dopant gas is stopped, theinterfacial layer 18 is formed under the hydrogen gas atmosphere.

[0057] The transparent substrate 11 may be made of any kind of materialonly if the photovoltaic element 20 can exhibit the above-mentionedadvantage effect of the present invention. In view of mass production,it is desired that the transparent substrate 11 is made of a polymerfilm having a glass-transition temperature (Tg) of 150° C. or below.PEN, PES, and PET may be exemplified as the polymer film.

[0058] The first transparent conductive film 12-1 and the secondtransparent conductive film 12-2 have preferably their respectiveamorphous structures. In this case, the above intermediate layer 17 canexhibit the reduction resistance for the transparent conductive films12-1 and 12-2. If the transparent substrate is made of the polymer film,the transparent conductive films 12-1 and 12-2 can have the amorphousstructures because they are required to be formed at low temperature of100° C. or below due to the heat sensitivity of the polymer film.

[0059] Although the photovoltaic elements 20 and 30 shown in FIGS. 2 and3 has two transparent conductive films composed of the first transparentconductive film 12-1 and the second transparent conductive film 12-2, itmay have single transparent conductive film.

[0060] If the first transparent conductive film 12-1 is made of ITO ortin oxide which have their respective larger electric conductivity, andthe second transparent conductive film 12-2 is made of zinc oxide whichhas larger plasma resistance, the open circuit voltage (Voc) of thephotovoltaic element 20 can be more enhanced without the degradation ofthe properties of the photovoltaic element 20.

[0061] The backside electrode 16 may be made, of a well known metallicmaterial such as Al, Ag or Ti, by a well known film-forming techniquesuch as a sputtering method or a vacuum evaporation method. The backsideelectrode 16 may be also made by a screen printing method using ametallic paste made of the above metallic material.

[0062] In the case of making the semiconductor layers 13, 14 and 15 andthe intermediate layer 17 of the silicon material, it is desired that atleast one of the first transparent conductive film 12-1 and the secondtransparent conductive film 12-2 is electrically grounded during theformation process of the above each layer if the each layer has anoxygen impurity concentration of 8×10¹⁸/cm₃ or over, a carbon impurityconcentration of 4×10¹⁸/cm³ or over, or a nitrogen impurityconcentration of 8×10¹⁷ ¹⁷/cm³ or over.

[0063] In this case, even though the above each layer includes muchimpurities such as oxygen elements and carbon elements, the photovoltaicelement can have its sufficient open circuit voltage (Voc) and the curvefill factor (FF).

[0064] It is considered as since the amount of the impurities in theabove each layer is not increased, the existence condition of theimpurities at the silicon network of the each layer may be changed orthe number of the dangling bond of the each layer may be decreasedthrough the change of the electric charge condition of a surface for theeach layer to be formed.

[0065] It is considered that the above impurities arise from the gaseouselements and moisture elements of the polymer film to constitute thetransparent substrate or the adhesive agent and the adhesive tape to fixthe transparent substrate to a supporter.

EXAMPLES

[0066] This invention will be concretely described with reference toExamples.

Example 1

[0067] In this example, the photovoltaic element shown in FIG. 2 wasfabricated.

[0068] An ITO film as the first transparent conductive film 12-1 wasformed in a thickness of 50 nm on a PEN film as the transparentsubstrate 11 on the condition that the Ar gas pressure was set to be 0.4Pa, and the oxygen gas pressure was set to be 0.08 Pa, and theintroducing electric power was set to be 0.3W/cm². The sheet resistanceof the ITO film formed according to the same condition was 150 Ω/□.Then, a zinc oxide film as the second transparent conductive film 12-2was formed in a thickness of 25 nm sequentially without the exposure toan atmosphere on condition that the Ar gas pressure was set to be 0.53Pa, and the introducing electric power was set to be 0.79W/cm². Thesheet resistance of the zinc oxide film formed according to the samecondition was 1 kΩ/□.

[0069] Then, the intermediate layer 17 was formed, in a differentchamber, in a thickness of 4 nm by a PECVD method on the condition thatthe substrate temperature was set to be 120° C., and the flow ratio ofAr gas/SiH₄ gas was set to be 300 sccm/3 sccm, and the total pressurewas set to be 56.65 Pa, and the introducing electric power was set to be90 mW/cm².

[0070] Subsequently, the p-type semiconductor layer 13 was formed in athickness of 6 nm by a PECVD method on the condition that the substratetemperature was set to be 120° C., and the flow ratio of B₂H₆ gas/H₂gas/SiH₄ gas was set to be 0.02 sccm/800 sccm/4 sccm, and the totalpressure was set to be 266.6 Pa, and the introducing electric power wasset to be 180 mW/cm².

[0071] Then, the intrinsic semiconductor layer 14 was formed, in adifferent chamber, in a thickness of 600 nm by a PECVD method on thecondition that the substrate temperature was set to be 160° C., and theflow ratio of H2 gas/SiH₄ gas was set to be 500 sccm/50 sccm, and thetotal pressure was set to be 133.3 Pa, and the introducing electricpower was set to be 50 mW/cm².

[0072] Subsequently, the n-type semiconductor layer 15 was formed, in adifferent chamber, in a thickness of 30 nm by a PECVD method on thecondition that the substrate temperature was set to be 160° C., and theflow ratio of PH₃ gas/H₂ gas/SiH₄ gas was set to be 0.06 sccm/500 sccm/5sccm, and the total pressure was set to be 133.3 Pa, and the introducingelectric power was set to be 60 mW/cm².

[0073] Next, the backside electrode 16 was made of an Al material in adifferent chamber by a vacuum evaporation method to fabricate thephotovoltaic element 20.

[0074] The electric property of the photovoltaic element 20 was measuredby irradiating a fluorescent light having 2101x into the photovoltaicelement 20 from the transparent substrate 11, and thus measured electricproperty was listed in Table 1.

Example 2

[0075] Except that the intermediate layer 17 was formed in a thicknessof 6 nm on the condition that the substrate temperature was set to be160° C., and the flow ratio of Ar gas/SiH₄ gas was set to be 300 sccm/3sccm, and the total pressure was set to be 200 Pa, and the introducingelectric power was set to be 90 mW/cm², the photovoltaic element 20 wasformed by the same manner as in Example 1. Then, the electric propertyof the photovoltaic element was measured by the same manner as inExample 1. The measured electric property was listed in Table 1.

Example 3

[0076] Except that the intermediate layer 17 was formed in a thicknessof 4 nm on the condition that the substrate temperature was set to be140° C., and the flow ratio of H₂ gas/Ar gas/SiH₄ gas was set to be 30sccm/300 sccm/3 sccm, and the total pressure was set to be 200 Pa, andthe introducing electric power was set to be 90 mW/cm², the photovoltaicelement 20 was formed by the same manner as in Example 1. Then, theelectric property of the photovoltaic element was measured by the samemanner as in Example 1. The measured electric property was listed inTable 1.

Example 4

[0077] Except that the intermediate layer 17 was formed in a thicknessof 7 nm on the condition that the substrate temperature was set to be140° C., and the flow ratio of B₂H₆ gas/H₂ gas/Ar gas/SiH₄ gas was setto be 0.02 sccm/10 sccm/300 sccm/3 sccm, and the total pressure was setto be 66.65 Pa, and the introducing electric power was set to be 90mW/cm², the photovoltaic element 20 was formed by the same manner as inExample 1. Then, the electric property of the photovoltaic element wasmeasured by the same manner as in Example 1. The measured electricproperty was listed in Table 1.

Example 5

[0078] Except that the intermediate layer 17 was formed in a thicknessof 5 nm on the condition that the substrate temperature was set to be130° C., and the flow ratio of Ar gas/SiH₄ gas was set to be 900 sccm/3sccm, and the total pressure was set to be 66.65 Pa, and the introducingelectric power was set to be 90 mW/cm², the photovoltaic element 20 wasformed by the same manner as in Example 1. Then, the electric propertyof the photovoltaic element was measured by the same manner as inExample 1. The measured electric property was listed in Table 1.

Example 6

[0079] Except that the intermediate layer 17 was formed in a thicknessof 6 nm on the condition that the substrate temperature was set to be130° C., and the flow ratio of Ar gas/SiH₄ gas was set to be 300 sccm/3sccm, and the total pressure was set to be 66.65 Pa, and the introducingelectric power was set to be 43 mW/cm², the photovoltaic element 20 wasformed by the same manner as in Example 1. Then, the electric propertyof the photovoltaic element was measured by the same manner as inExample 1. The measured electric property was listed in Table 1.

Comparative Example 1

[0080] Except that the p-type semiconductor layer 13 was formed in athickness of 10 nm without the intermediate layer, a photovoltaicelement was fabricated by the same manner as in Example 1. Then, theelectric property of the photovoltaic element was measured by the samemanner as in Example 1. The measured electric property was listed inTable 1.

Comparative Example 2

[0081] Except that the p-type semiconductor layer 13 was formed in athickness of 10 nm without the intermediate layer on the condition thatthe substrate temperature was set to be 140° C., and the flow ratio ofB₂H₆ gas H₂ gas/Ar gas/SiH₄ gas was set to be 0.02 sccm/10 sccm/300sccm/3 sccm, and the total pressure was set to be 66.65 Pa, and theintroducing electric power was set to be 90 mW/cm², a photovoltaicelement was fabricated by the same manner as in Example 1. Then, theelectric property of the photovoltaic element was measured by the samemanner as in Example 1. The measured electric property was listed inTable 1.

Comparative Example 3

[0082] Except that the intermediate layer 17 was formed in a thicknessof 6 nm on the condition that the substrate temperature was set to be160° C., and the flow ratio of H₂ gas/Ar gas/SiH₄ gas was set to be 100sccm/300 sccm/3 sccm, and the total pressure was set to be 200 Pa, andthe introducing electric power was set to be 90 mW/cm², a photovoltaicelement was fabricated by the same manner as in Example 1. Then, theelectric property of the photovoltaic element was measured by the samemanner as in Example 1. The measured electric property was listed inTable 1.

Example 7

[0083] In this example, the photovoltaic element shown in FIG. 3 wasfabricated.

[0084] Except that the interfacial layer 18 was formed in a thickness of5 nm by a PECVD method on the condition that the substrate temperaturewas set to be 120° C., and the flow ratio of H₂ gas/SiH₄ gas was set tobe 500 sccm/4 sccm, and the total pressure was set to be 133.3 Pa, andthe introducing electric power was set to be 50 mW/cm, the photovoltaicelement was fabricated by the same manner as in Example 1. In this case,the intermediate layer 17, the p-type semiconductor layer 13 and theinterfacial layer 18 were formed in the same chamber, and themanufacturing period was 24 minutes. Moreover, the manufacturing periodof the intrinsic semiconductor layer 14 was 35 minutes. Then, theelectric property of the photovoltaic element was measured by the samemanner as in Example 1. The measured electric property was listed inTable 1.

Example 8

[0085] Except that the intermediate layer 17 and the p-typesemiconductor layer 13 were formed in a thickness of 10 nm, respectivelywithout the interfacial layer 18, a photovoltaic element was fabricatedby the same manner as in Example 10. Then, the electric property of thephotovoltaic element was measured by the same manner as in Example 1.The measured electric property was listed in Table 1.

Comparative Example 4

[0086] Except that the p-type semiconductor layer 13 were formed in athickness of 10 nm, respectively without the interfacial layer 18, aphotovoltaic element was fabricated by the same manner as in Example 7.Then, the electric property of the photovoltaic element was measured bythe same manner as in Example 1. The measured electric property waslisted in Table 1. TABLE 1 Open circuit Short-circuit current voltage(Voc) Curve fill factor (μA/cm²) (V) (F. F) Example 1 15.2 0.64 0.71Example 2 15.4 0.64 0.72 Example 3 15.3 0.63 0.71 Example 4 15.1 0.640.70 Example 5 15.3 0.63 0.70 Example 6 15.2 0.63 0.71 Example 7 — 0.66— Example 8 — 0.64 — Comparative 15.0 0.58 0.69 Example 1 Comparative14.8 0.59 0.69 Example 2 Comparative 14.8 0.59 0.69 Example 3Comparative — 0.58 — Example 4

[0087] As is apparent from Examples 1-8 and Comparative Examples 1, 2and 4, the photovoltaic elements with their respective intermediatelayers can have enhanced open circuit voltages (Voc), respectively.Moreover, as is apparent from Examples 1-6 and Comparative Examples 1and 2, the electric properties such as short-circuit current and curvefill factor (FF) of the photo-voltaic elements are enhanced as the opencircuit voltages (Voc) are increased.

[0088] Moreover, as is apparent from Examples 1-8 and ComparativeExample 3, when the intermediate layer is formed under the hydrogen gasatmosphere beyond the hydrogen concentration according to the presentinvention, the open circuit voltage (Voc) is degraded, and theshort-circuit current and the curve fill factor (FF) are also degraded.

[0089] Then, as is apparent from Example 7 and Examples 1-6, 8, thephoto-voltaic element having the interfacial layer can have moreenhanced open circuit voltage (Voc).

Comparative Example 5

[0090] A comparative photovoltaic element was fabricated for evaluatingthe crystallinity of the above photovoltaic element according to thepresent invention.

[0091] First of all, an Al film was formed in a thickness of 500 nm onthe PEN film by a DC sputtering method on the condition that the Ar gaspressure was set to be 0.5 Pa, and the sputtering electric power was setto be 6.7 W/cm₂. Then, a SUS 304 film was formed in a thickness of 5 nmon the condition that the Ar pressure was set to be 0.5 Pa, and thesputtering electric power was set to be 0.35 W/cm². Subsequently, theintermediate layer 17, the p-type semiconductor layer 13, the intrinsicsemiconductor layer 14 and the n-type semiconductor layer 15 are formedin turn by the same manner as in Example 1.

[0092] Then, the crystallinity of the photovoltaic element fabricated inExample 4 was examined from the side of the n-type semiconductor layerside by Raman spectroscopic analysis. The result is presented FIGS. 4and 5.

[0093] As is apparent from FIGS. 4 and 5, in the n-type semiconductorlayer, there is no peaks originated from the bond between hydrogenelement and silicon element around 2000 cm⁻¹ and originated fromamorphous silicon around 500 cm⁻¹, and there is a peak originated fromcrystalline silicon around 500 cm⁻¹.

[0094] Then, the crystallinity of the photovoltaic element fabricated incomparative Example 5 was examined from the n-type semiconductor layerby Raman spectroscopic analysis. The result is presented in FIGS. 6 and7.

[0095] As is apparent from FIGS. 6 and 7, in the n-type semiconductorlayer, there is peaks originated from the bond between hydrogen elementand silicon element around 2000 cm⁻¹ and originated from amorphoussilicon around 500 cm⁻¹. As a result, it is turned out from FIGS. 4-7that the n-type semiconductor layer of the photovoltaic elementaccording to the present invention has a good crystallinity.

Example 9

[0096] Except that before the p-type semiconductor layer 13 is formed,the photovoltaic assembly was plasma-treated for three minutes at asubstrate temperature of 120° C. in a hydrogen-reduction atmosphere of100% hydrogen concentration, the photovoltaic element 20 was fabricatedby the same manner as in Example 1. In the plasma-treatment, an electricpower of 60 mW/cm² with a high frequency of 13.56 MHz was introducedinto the hydrogen-reduction atmosphere under the hydrogen gas flow rateof 1000 sccm and the total pressure of 66.65 Pa to generate a hydrogenplasma. Then, the electric property of the photovoltaic element wasmeasured by the same manner as in Example 1. The measured electricproperty was listed in Table 2.

Example 10

[0097] Except that before the p-type semiconductor layer 13 is formed,the photovoltaic assembly was plasma-treated for six minutes at asubstrate temperature of 140° C. in a hydrogen-reduction atmosphere of100% hydrogen concentration, the photovoltaic element 20 was fabricatedby the same manner as in Example 3. In the plasma-treatment, an electricpower of 100 mW/cm² with a high frequency of 13.56 MHz was introducedinto the hydrogen-reduction atmosphere under the hydrogen gas flow rateof 1000 sccm and the total pressure of 266.6 Pa to generate a hydrogenplasma. Then, the electric property of the photovoltaic element wasmeasured by the same manner as in Example 1. The measured electricproperty was listed in Table 2. TABLE 2 Open circuit Short-circuitcurrent voltage (Voc) Curve fill factor (μA/cm²) (V) (F. F) Example 915.6 0.64 0.72 Example 10 15.6 0.63 0.71

[0098] It is turned out from Examples 1-6 and 9-10 in Tables 1 and 2that the photovoltaic elements having their respective plasma-treatedintermediate layers can have more enhanced short-circuit currents,respectively.

Example 11

[0099] Except that the first transparent conductive film 12-1 and thesecond transparent conductive film 12-2 are electrically grounded duringthe formation of the intermediate layer 17, the p-type semiconductorlayer 13, the intrinsic semiconductor layer 14 and the n-typesemiconductor layer 15, the photovoltaic element 20 was fabricated bythe same manner as in Example 1. Then, the electric property of thephotovoltaic element was measured by the same manner as in Example 1.The measured electric property was listed in Table 3.

[0100] Moreover, the impurity kind and the impurity concentration ineach layer of the photovoltaic element were identified by SIMS, and arelisted in Table 3. In this case, the impurity concentration is averagedthroughout the each layer.

[0101] In comparison, the electric properties and the impurityconcentration of each layer of the photovoltaic element fabricated inExample 1 are listed in Table 3. TABLE 3 Short- Open circuit circuitCurve Impurity current voltage fill Oxygen Carbon Nitrogen (μA/ (Voc)factor (atoms/ (atoms/ (atoms/ cm²) (V) (F. F) cm³) cm³) cm³) Exam- 15.20.64 0.71 2 × 10¹⁹ 6 × 10¹⁸ 1 × 10¹⁸ ple 1 Exam- 15.2 0.65 0.73 2 × 10¹⁹6 × 10¹⁸ 1 × 10¹⁸ ple 11

[0102] As is apparent from Table 3, although the impurity concentrationsof the intermediate layer and the semiconductor layers of thephotovoltaic element in Example 11 are equal to those of thephotovoltaic element in Example 1, the photovoltaic element has enhancedelectric properties.

[0103] This invention is not limited to the above embodiments and everykind of variation and modification may be made without departing fromthe scope of the present invention.

[0104] For example, in the above embodiment, the first conduction-typesemiconductor layer is composed of the p-type semiconductor layer andthe second conduction-type semiconductor layer is composed of the n-typesemiconductor layer, but the other way around may be done.

[0105] As mentioned above, according to the present invention, eventhough the photovoltaic element has, on the transparent substrate, anopposed electrode made of the transparent conductive film to thebackside electrode, it can have the open circuit voltage (voc) almostequal to that of a photovoltaic element having an opposed electrode madeof a metallic material.

What is claimed is:
 1. A photovoltaic element comprising a substrate, atransparent conductive film provided on the substrate, an intermediatelayer, provided so as to cover the transparent conductive film, made ina hydrogen gas atmosphere of 15 volume % or below hydrogenconcentration, a first conduction-type semiconductor layer provided onthe intermediate layer, an intrinsic semiconductor layer provided on thefirst conduction-type semiconductor and a second conduction-type,different from the first conduction-type, semiconductor layer providedon the intrinsic semiconductor layer.
 2. A photovoltaic element asdefined in claim 1 , wherein the intermediate layer is made in thehydrogen gas atmosphere of 6 volume % or below hydrogen concentration.3. A photovoltaic element as defined in claim 1 or 2 , wherein theintermediate layer is made by a plasma CVD method.
 4. A photovoltaicelement as defined in claim 1 or 2 , wherein the intermediate layer ismade of the same material as that of any one of the firstconduction-type semiconductor layer, the intrinsic semiconductor layerand the second conduction-type semiconductor layer.
 5. A photovoltaicelement as defined in claim 1 or 2 , wherein the intermediate layer ismade of the same material as that of the first conduction-typesemiconductor layer.
 6. A photovoltaic element as defined in claim 4 ,wherein the intermediate layer is made of a silicon material, and thethickness of the intermediate layer is set to be within 0.5-15 nm.
 7. Aphotovoltaic element as defined in claim 1 or 2 , wherein a surface ofthe intermediate layer is plasma-treated in a hydrogen-reductionatmosphere.
 8. A photovoltaic element as defined in claim 1 or 2 ,further comprising an interfacial layer between the firstconduction-type semiconductor layer and the intrinsic semiconductorlayer.
 9. A photovoltaic element as defined in claim 8 , wherein theinterfacial layer is made of the same material as that of any one of thefirst conduction-type semiconductor layer, the intrinsic semiconductorlayer and the second conduction-type semiconductor layer.
 10. Aphotovoltaic element as defined in claim 9 , wherein the interfaciallayer is made of the same material as that of the first conduction-typesemiconductor layer.
 11. A photovoltaic element as defined in claim 9 ,wherein the interfacial layer is made of a silicon material, and thethickness of the interfacial layer is set to be within 0.5-8 nm.
 12. Aphotovoltaic element as defined in claim 1 or 2 , wherein thetransparent conductive film is composed of a first transparentconductive film and a second transparent conductive film.
 13. Aphotovoltaic element as defined in claim 1 or 2 , wherein thetransparent conductive film has an amorphous structure.
 14. Aphotovoltaic element as defined in claim 1 or 2 , wherein the substrateis made of a polymer film.
 15. A method for manufacturing a photovoltaicelement comprising the steps of: forming a transparent conductive filmon a substrate, forming an intermediate layer so as to cover thetransparent conductive film in a hydrogen gas atmosphere of 15 volume %or below hydrogen concentration, and forming, on the intermediate layer,a first conduction-type semiconductor layer, an intrinsic layer and asecond conduction-type, different from the first conduction-type,semiconductor layer in turn.
 16. A method for manufacturing aphotovoltaic element as defined in claim 15 , wherein the intermediatelayer is formed in the hydrogen gas atmosphere of 6 volume % or belowhydrogen concentration.
 17. A method for manufacturing a photovoltaicelement as defined in claim 15 or 16 , wherein the intermediate layer isformed by a plasma CVD method.
 18. A method for manufacturing aphotovoltaic element as defined in claim 15 or 16 , wherein theintermediate layer is formed of the same material as that of any one ofthe first conduction-type semiconductor layer, the intrinsicsemiconductor layer and the second conduction-type semiconductor layer.19. A method for manufacturing a photovoltaic element as defined inclaim 18 , wherein the intermediate layer is formed of the same materialas that of the first conduction-type semiconductor layer.
 20. A methodfor manufacturing a photovoltaic element as defined in claim 18 ,wherein the intermediate layer is made of a silicon material, and thethickness of the intermediate layer is set to be within 0.5-15 nm.
 21. Amethod for manufacturing a photovoltaic element as defined in claim 15or 16 , wherein a surface of the intermediate layer is plasma-treated ina hydrogen-reduction atmosphere.
 22. A method for manufacturing aphotovoltaic element as defined in claim 15 or 16 , further comprisingthe step of forming an interfacial layer between the firstconduction-type semiconductor layer and the intrinsic semiconductorlayer.
 23. A method for manufacturing a photovoltaic element as definedin claim 15 or 16 , wherein the interfacial layer is made of the samematerial as that of any one of the first conduction-type semiconductorlayer, the intrinsic semiconductor layer and the second conduction-typesemiconductor layer.
 24. A method for manufacturing a photovoltaicelement as defined in claim 23 , wherein the interfacial layer is madeof the same material as that of the first conduction-type semiconductorlayer.
 25. A method for manufacturing a photovoltaic element as definedin claim 23 , wherein the interfacial layer is made of a siliconmaterial, and the thickness of the interfacial layer is set to be within0.5-8 nm.
 26. A method for manufacturing a photovoltaic element asdefined in claim 15 or 16 , wherein the transparent conductive film iscomposed of a first transparent conductive film and a second transparentconductive film, and the first transparent conductive film is formed onthe substrate, and the second transparent conductive film is formed onthe first transparent conductive film.
 27. A method for manufacturing aphotovoltaic element as defined in claim 15 or 16 , wherein thetransparent conductive film is formed at a substrate temperature of 100°C. or below.
 28. A method for manufacturing a photovoltaic element asdefined claim 15 or 16 , wherein at least one layer of the intermediatelayer, the first conduction-type semiconductor layer, the intrinsicsemiconductor layer, the second conduction-type semiconductor layer isformed of a silicon material, and during the formation of the at leastone layer, the transparent conduction film is electrically grounded whenthe at least one layer includes oxygen impurities of 8×10¹⁸/cm³ or overconcentration, carbon impurities of 4×10¹⁸/cm³ or over, or nitrogenimpurities of 8×10¹⁷/cm³ or over.